The goal of this project is to use the snake venom post synaptic neurotoxins to identify and to probe the stereochemistry of the toxin binding site on the acetylcholine receptor. This novel approach employs detailed information about a specific region on the toxin interactive surface, and the identification of the segment of receptor alpha subunit chain which binds there. Specific peptide fragments from the receptor alpha subunit sequence will be synthesized. Interactions between these synthetic peptides and venom toxins, initially erabutoxin b, will be studied by H-1 NMR. The structures of any complexes formed will be established by x-ray crystal structure analysis. The 3-dimensional x-ray structure analyses of two neurotoxins will be completed (erabutoxin c) and determined (laticotoxin) by the use of the molecular replacement method. The purpose is two-fold: 1) to develop further experience with this method, which will be used to determine the structures of the peptide complexes 2) to confirm that significant features of the detailed erabutoxin b structure are common to these toxins. In addition, results of molecular mechanics calculations on the toxin structures will be analyzed in terms of energy requirements for specific conformational shifts. The crystal structures of small rigid molecules as antagonists or agonists of the receptor will be determined as needed. A knowledge of the 3-dimensional structure of the toxin-binding region on the receptor will be useful in understanding neuromuscular transmission - both normal and pathological.